Embodiments of the present invention relate to wireless ultra-wideband (UWB) ranging and localization systems, and in particular, to a concept for determining a time measure depending on a time of arrival of a pulse signal having a sequence of pulses from a transmitter. Further embodiments of the present invention relate to an energy receiver architecture for UWB ToA (time of arrival) estimation.
Ultra-wideband Impulse Radio (UWB-IR) has several unique characteristics that make it a promising candidate for future wireless localization. The large absolute bandwidth, in the US from 3.1 to 10.6 GHz and in Europe from 6 to 8.5 GHz, corresponds to a very fine time resolution in the order of hundreds of picoseconds which translates to spatial resolution in the order of centimeters. The very fine time resolution allows a direct path to be easily distinguished from the reflected paths. This is of paramount importance in indoor environments where other localization systems suffer from the multipath phenomenon. The presence of low frequency components in the UWB signal spectrum enables penetration of the UWB signals through the walls. UWB devices are permitted to transmit very weak signals so that other systems sharing the same spectrum, including for instance IEEE 802.11a WLANs, are protected. Low interference, possibility of high device density and low probability of detection and interception (LPD/I) are these characteristics of the UWB technology that are of particular importance for military applications. Furthermore, the UWB technology promises prospects for long-life battery operation and low cost mainly thanks to simple transceiver implementations.
However, the same properties provide design challenges, such as high sampling rate, synchronization and power control. Portable devices impose strict requirements on the size and shape of the antenna which has to radiate effectively in a wide frequency band and under varying propagation conditions sometimes including near-field, e.g. when carried on the human body or close objects. To ensure a further development of the UWB technology and a wide presence of its products on the commercial market of tomorrow, these challenges may be properly addressed and resolved.
Reception of UWB signals poses challenges in the receiver structure. According to the state-of-the-art, an optimal estimate of ToA may be performed by means of a conventional matched filter/correlation receiver.
An example of a correlating receiver is presented in US 2005/0069059 A1, where a pulse sequence energy estimator and a complicated architecture may be used. US 2003/0227961 A1 describes a RAKE architecture for an UWB receiver. The architecture is based on a bank of switched capacitors and involves using high sampling rate.
A low complexity alternative to the matched filter or RAKE receiver is the energy detection (ED) receiver. WO 2005/074150 A1 presents a non-coherent receiver based on the ED architecture that is suitable for communication applications with PAM (pulse amplitude modulation) and PPM (pulse position modulation) schemes. Here, it is proposed to perform a weighting integration operation. U.S. Pat. No. 7.526.048 B2 describes a method for selecting the threshold in the ED-receiver based ToA ranging system. It is proposed to use kurtosis of the signal after an integration step in the ED. Another method of setting the threshold is presented in Ismail Guvenc and Zafer Sahinoglu, “Threshold-Based TOA Estimation for Impulse Radio UWB Systems”, IEEE International Conference on Ultra-Wideband. ICU 2005. This method is based on normalized value according to the signal-to-noise value and integration window size.
However, a general problem of known receivers is that they are characterized by relatively low time/distance resolution and have a relatively complex structure.